Sportsman Flyer Build

[Chainlube]

The porting is fairly easy to do too. When you look into the port, out to in direction, you should see a pretty clear shot into the cylinder. Just remove the material that interferes with the path. Pay close attention to the ledge just inside the port, if you put your finger in there you'll be able to feel a sharp-ish ledge, just file it off. The intake side you just want it to be rough anyway, usually the polish is for the exhaust side.

 

[Deleted member 25783]

I started this new hot rod engine. April 7, 2021

Shane machines down the protruding part of both valve guides in the ports using a special to me 6mm piloted counter bore that I don't have.
Plan B. The valve guides are press fitted into the head, so I carefully drove them flush in the port chambers.
Made the port polish much easier overall. With one caveat. The added length of the intake valve guide in the rocker arm chamber will not allow the intake valve seal to set at the designed height.
The valve guide will be milled and deburred lightly. Done so to allow valve seal a proper fit.
Tom

 

[Deleted member 25783]

Things are coming in for the 79cc Predator power boost project. AGK 18# springs and full gasket set.
Metal head gasket, I reckon so you don't blow a gasket.

 

[Deleted member 25783]

79cc Predators are alleged to produce 3hp. But it can be increased to it is claimed optimum AGK claims to 5 to 7 horse power?

The total weight of a Sportsman Flyer 80 is not specified but they are a weighty machine for reasons of safety and durability. We have roads in the Kettle Moraine area of S.E. Wisconsin that going East West take the Eskers at a right angle = steep 30degree 200 ft climbs. Flyer80 struggles to mount without a good running start stock engine. More power is the ticket!

You can send your 79cc Predator engine head to AGK, get a .050” head deck, to up compression, and port and polish, adding stronger 18lb valve springs are needed if you remove the governor.

19mm Mikuni clone carb is a given. Stock Predator carbs do not have flow anywhere equal to a 19mm Mikuni clones.

The only other extreme and costly mod I am doing, is replacing the cast iron flywheel with a ARC Racing billet aluminum flywheel. Keyway cut to a extra 4 degree spark advance totaling a 28 degrees of advance.

Today the ARC 6671 flywheel came by post. It is a CNC machined thing of beauty. Embellished with engraving which will
be unseen as I will be using the pull start blower housing this time around to take advantage of the finned flywheel.
Couple of poor photos. I got a pro photog buddy. Where is that rascal?

 

[Deleted member 25783]

AGK has a flywheel installation vid. ARC Racing - Video #1, Billet Flywheel Installation. - YouTube
The taper lapping portion was something I had not considered. Or was woodruff key orientation.
Thirty minutes of information I would not have found. All of it invaluable. And a Georgian accent for flavor.
Tom

 

[Deleted member 25783]

Just from video #1. lapping in the flywheel / crankshaft taper contact area never crossed my mind. That AGK does not give a hoot for woodruff keys is telling. It looks like AGK is content with only 60% contact superseding key positioning. Allowing metal to metal contact grip to supersede key retention.
Now I gotta hunt down the two tins of water soluble lapping compound lurking somewhere in the shop.
The other interesting value of a keyless flywheel according to the video is setting way beyond the keyed timing advance.

So, this will be my approach. Lap the mating flywheel and crankcase surfaces, but start at the keyed position.
If someone has empirical experience with spark advance beyond 28degrees BTDC. let me know.
Lapping the mating flywheel and crankshaft surfaces.
I surely thought 54 foot pounds torque could draw two tapers into full mate.
Tom

 

[Deleted member 25783]

Made a copper scraper and cleaned up the clinging gasket on the crankcase.
Still have to clean up the side cover.
Made a tap guide block to squarely tap 5/16-18 four holes in the tooling plate for mounting the engine head right side up.
When I pressed the valve guides flush with the valve pockets, the valve guides got taller by 2.5mm top side.

If I don't cut down 2.5mm of the valve guide of intake the valve seal flange will not set flush on the spring boss.
After that, flush the crankcase. Amazing all the nasty metal grunge in a fresh engine.
Give the modified head a good soapy wash and rinse. Reassemble the valve train contained in the engine.
The fussiest part and important part to me is the valve lash adjustment. AGK spec's .004" for intake and exhaust.
If I get anything done tomorrow after our Sunday driving Miss Daisy (Mona) I can only hope.
Question: Does anyone use Permatex on their gaskets on a reassemble? Factory sure doesn't.
Tom

 

[Deleted member 25783]

Once I clamped the tooling plate head assembly in the Mill vise I was able to mill down the intake valve guide 1.9mm.
Allowing the intake valve seal flange to seat properly on the valve spring boss.
This was done after I pressed the valve guides flush in their respective intake and exhaust port pockets.
Monday is going to be soap and water washing day. If you never have soap and rinsed aluminum. Be surprised.
Tom

 

[Deleted member 25783]

Scored 1/16-27 NPT plug for sealing the governor shaft hole in the crankcase. 90 cents. A buck would be even change.
Tom

 

[Deleted member 25783]

Knocking the stock cast iron flywheel off the crankshaft, and begin the lapping process to ensure proper fit of the ARC flywheel to the Predator 79cc crankshaft. Youtube does decent documentation both AGK and ARC.
The ARC video does not dwell on the time it takes for a proper lap job.
Fifty years of experience lets me say. 75% contact is good, 90% contact better in steel. Aluminum unlike steel compressed has no spring-back.
Tom